Velo 2G Gripper

Submitted by Anonymous on Thu, 10/11/2012 - 00:51

As part of our research and development work at Willow Garage, we’ve recently been exploring new gripper designs and grasping strategies. We’d like to share some early results involving a new gripper that we’ve recently developed and tested. While parallel grasps are effective on a wide range of objects and tasks, adding the ability to envelop objects can greatly increase the stability of the grasp in many situations. We explored the design space aiming to achieve both of these capabilities.

The Velo 2G gripper, which we are presenting today, has two fingers with two joints each, and is tendon-driven. Aiming to reduce the complexity and potential cost, we used a single actuator, resulting in an underactuated design. The gripper executes fingertip or enveloping grasps by passively adapting to the shape of the grasped object. Extension is passive, provided by springs.

The route of the tendons and the magnitude of the extension forces are optimized to execute both types of grasps, and to passively transition from one to the other based on the shape of the grasped object. The forces applied to the target object are also optimized to result in stable grasps in a large set of possible configurations. The kinematic parameters, such as the dimensions of the links and the joint limits, are optimized to execute enveloping grasps on a large set of common household objects. Passive adaptation also allows the gripper to conform to asymmetric or irregular shapes.

For building the prototypes shown today, we explored multiple emerging 3D printing technologies. The palm and fingers are 3D printed in nylon using an SLS process. The actuator module consists of a single motor attached to a transmission built around a 3D printed recirculating ball screw. The use of 3D printing technologies has allowed us to quickly iterate over design improvements, while still providing the robustness needed for integration on mobile manipulators and early application research and development.